Ultrastructure of Goussia cruciata (Apicomplexa: Coccidia) infecting the liver of horse mackerel, Trachurus trachurus (L.), from Ibero-Atlantic waters

The ultrastructure of developmental stages of Goussia cruciata and the pathology they cause in the liver of Trachurus trachurus (Teleostei: Carangidae) caught off the Galician (North-West Spain) and Portuguese North Atlantic coasts are described. Each oocyst contained four ellipsoidal sporocysts, with two sporozoites. The sporocyst wall consisted of a thick and dense inner layer with transverse striations and a multi-lamellated outer layer formed by parallel dense internal bands alternating with lighter areas. The lamellae formed filamentous extensions of the wall. The sporocyst wall striation period was smaller than that observed in G. clupearum, which has a similar habitat. The dehiscence suture, characteristic of the genus, was present in the sporocysts of G. cruciata. The sporocysts were arranged in a symmetrical and characteristic cross shape. A large number of sporocysts with sporozoites were observed in direct contact with host liver cells. No macroscopic lesions were observed. In heavily infected fish, aggregations of oocysts were often enveloped in a 'yellow body' composed of amylopectin granules derived from the parasite and necrotic or aggregated host cells. Degenerating parasites were frequently observed in liver tissue. Host inflammatory cells were accumulated near some oocysts. The ultrastructure of the parasite, together with its strict host specificity, confirmed G. cruciata as a separate and valid species.     

The effect of Eimeria sp. infection on the condition of blue whiting, Micromesistius poutassou (Risso)

Abstract. Eimeria sp. infection of blue whiting, Micromesistius poutassou (Risso), taken to the north and west of Scotland, was investigated with particular reference to the effect on host condition. Eimeria sp. is a parasite of the liver parenchyma and causes extensive lesions. Juvenile blue whiting were not found to be infected before the late 1-group stage, but all 308 adult (3- to 17-group) fish examined were infected. Condition factor ( k = 100 w/l³ ) showed a statistically significant decrease with increasing intensity of infection. Average value of liver weight, expressed as a percentage of total body weight, also decreased with increasing intensity of infection. It is concluded that Eimeria sp. infection is a major factor contributing to loss of condition in blue whiting from the study area. The loss of weight in fish with moderate-to-heavy infections was estimated at from 6 to 10%; this figure does not take account of mortalities resulting from Eimeria infection nor does it take account of the most heavily infected fish which could not be included in the analysis because sufficiently accurate estimates of the large numbers of oocysts present were not made.     

Coccidiosis due to Goussia lomi (Protista: Apicomplexa) in aquarium-reared Murray cod, Maccullochella peeli (Mitchell), (Percichthyidae)

Abstract. Intestinal parasitism by the coccidian Goussia lomi was associated with morbidity and histological lesions in aquarium-reared Murray cod fry, Maccullochella peeli (Mitchell), at a hatchery near Narrandera, New South Wales, Australia. Coccidial infection was not found in pond-reared Murray cod of the same age, nor in trout cod, M. macquariensis (Cuvier & Valenciennes), reared under similar conditions at the same hatchery. Overcrowding may have predisposed Murray cod in aquaria to heavy infection with G. lomi. Clinical coccidiosis was expressed in a small proportion of infected fish. Large numbers of coccidial developmental forms were detected histologically in the intestinal mucosa of affected fish in association with a necrotic enteropathy. Using a method of intestinal trypsin digestion and flotation, 2000 coccidial oocysts were counted in one 0-05g fish.     

A new species of Goussia (Apicomplexa, Coccidia) in the kidney tubules of the cod, Gadus morhua L.

Abstract. Segments of the kidney tubules of about 16% of cod caught in the approaches to Halifax Harbour were found to contain a coccidian parasite. Macrogametes developed in an epicellular position, and microgamonts, unsporulated and sporulating oocysts, and free sporocysts, were found in the lumen of the kidney tubule. The epithelial cells of the kidney tubules were damaged and granulomas often formed around infected tubules. The presence of a suture dividing the sporocyst wall into two valves could only be determined using electron microscopy. Other coccidians which have been placed in the genus Eimeria because sutures could not be seen using light microscopy, although no Stieda body was present, may also belong to the genus Goussia. No other coccidians have been reported in the kidney tubules of marine fish, and the name Goussia spraguei sp. nov., is proposed.     

Cultivation of Trypanosoma danilewskyi (Laveran & Mesnil, 1904) in serum-free medium and assessment of the course of infection in goldfish, Carassius auratus (L.)

Abstract. Purification and in vitro cultivation techniques were developed for the fish haemoflagellate, Trypanosoma danilewskyi. The parasites were isolated and purified from the peripheral blood of experimentally infected goldfish, using a combination of Ficolt-paque gradient centrifugation to remove fish red blood cells and in vitro incubation to remove the remaining fish leucocytes. A serum-free culture medium for T. danilewskyi supported both short- and long-term cultivation of the haemoflagellates. The serum-free medium is a mixture of reagents available commercially: Leibovitz's L-15 medium, Dulbecco's Modified Eagle Medium and Hank's balanced salt solution. The doubling time was calculated to be 44.4 × 7.8h. Typically, a two- to five-fold increase in the number of cultured parasites was observed on day 7 after subculture with 1 × 10⁶ and 5 × 10⁵ trypanosomes ml⁻¹, respectively. When administered to fish, the in vitro -derived parasites caused an infection and pathology whose characteristics were similar to those observed following infection with trypanosomes obtained from infected goldfish. The freshly isolated and in vitro -grown parasites were successfully cryoprescrvcd in the culture medium containing 10% glycerine at −80°C for at least 3 months. Although the viability of the parasite decreased by 40–50% after thawing, cryoprcserved parasites retained the ability to infect goldfish.
Correspondence: Dr M. Belosevic, Associate Professor, Department of Zoology, CW-312 Biological Sciences Building, University of Alberta, Edmonton, AB, Canada T6G 2E9.     

Goussia auxidis (Dogiel, 1948) (Apicomplexa: Calyptosporidae) from tuna (Pisces: Scombridae) in the South Pacific

Abstract. A coccidian identified as Goussia auxidis (Dogiel, 1948) is recorded for the first time from the liver and spleen of albacore, Thunnus alalunga; the liver of slender tuna, Allothunnus fallai , skipjack tuna, Katsuwonus pelamis and yellowfin tuna, T. albacares: and in the spleen of Scomber australasicus. All host fish were caught in the western and central South Pacific Ocean. Coccidian spores were not found in the liver of southern bluefin tuna, T. maccoyii , or butterfly tuna, Gasterochisma melampus.     

The pathology of Haplorchis pumilio (Looss, 1896) infections in cultured tilapias

Abstract. Haplorchis pumilio (Looss, 1896) is a common digenean parasite of many species of fish of economic importance and has been found to infect cultured Sarotherodon spp. Fry of S. spilurus (Günther), S. mossambicus (Peters) and S. galilaea (L.) were experimentally infected with cercariae of H. pumilio from natural infections of Melanoides tuberculata (Müller) from an East African fish farm. Large numbers of cercariae were lethal to the fry within a few hours. Histopathological examination showed that the most significant pathological effect was focal haemorrhages in skeletal muscles in heavily infected fish. Migration of cercariae was through connective tissue and the final location of the metacercariae was connective tissue associated with skeletal structures. Clusters of cysts occurred at the bases of fins and in the loose connective tissue of the head, but the reaction to encysted metacercariae was insignificant. The overall effect on growth performance and thus economic importance of H. pumilio infection was assessed. Growth studies showed no significant differences between specific growth rate, food conversion ratios and condition of infected and uninfected fish.     

Infection of the Carpathian brook lamprey (Eudontomyzon danfordi Regan, 1911) with a dermocystid parasite in the Tisza River Basin,Hungary

The Carpathian brook lamprey (Eudontomyzon danfordi Regan, 1911) is an endemic protected species of Cephalaspidomorphi in the Carpathian Basin. No parasites have become known from these jawless vertebrates to date. Here, the authors describe an infection from a single specimen manifesting in protuberant skin cysts 7–10 mm in diameter, scattered on the body surface. Similar dermal infection was observed in 25 of the 274 lampreys recorded in the population survey. Skin cysts filled with round spore-like structures of a dermocystid parasite were found. These particles measured 8–14 µm in diameter and had an about 0.5 µm thick wall, and containing mainly a granular mass and a relatively scarce plasma. No hyphae were recorded. Despite conspicuous morphological changes in the skin, no inflammatory reactions were found. The molecular analysis of 18S rDNA showed similarity to dermocystid species of several fish species but differed from them approximately by 2%. This is the first record of a dermocystid parasite infecting a jawless vertebrate.     

A new species of Pleistophora from big-eyes, Priacanthm tayenus Richardson, and P. macracanthus Cuvier and Valenciennes, from the South China Sea

Abstract. Pleistophora priacanthusis sp. nov. is described from big-eyes, Priacanthus tayenus and P. macracanthus , from the South China Sea. The clinical signs, prevalence, intensity and site of infection of the infected fish, the general effect of the parasite on the host, seasonal distribution and sex differences are reported. The morphology of cysts, spores, sporonts and the characteristic features of the new species using the light microscope are described.     

The effect of foraging and ontogeny on the prevalence and intensity of the invasive parasite Anguillicola crassus in the European eel Anguilla anguilla

Infection patterns of the invasive Anguillicola crassus nematode were investigated in a population of the European eel Anguilla anguilla where parasite invasion is very recent, Loch Lomond, Scotland. Intensity levels of the parasite were associated with differences in fish ontogeny and trophic ecology. Although eels foraged on both fish and invertebrates, individuals which were smaller and fed on invertebrates (>70% contribution to diet) were found to contain a greater number of swim bladder parasites compared to larger eel with a predominance of fish (>60% contribution) in their diet. Within affected fish, a significant negative relationship was found between fish length and parasite intensity, with smaller individuals having higher parasite intensity than larger individuals. This study indicates that food intake and infection risk are linked in this recently infected host–parasite system. From a management perspective increasing our understanding of how infection intensity and repeated exposure is linked to resource use in an ecosystem is important for the future management of this endangered species in Europe.     

The life cycle of Henneguya nuesslini Schuberg & Schroder, 1905 (Myxozoa) involves a triactinomyxon-type actinospore

The life cycle of the histozoic myxozoan parasite Henneguya nuesslini was investigated in two salmonid host species. Naive brown trout, Salmo trutta, and brook trout, Salvelinus fontinalis, were experimentally infected in two trials by triactinomyxon type actinospores from naturally infected Tubifex tubifex. In exposed common carp, Cyprinus carpio, no myxospore production was detected. The parasite formed cysts with mature myxospores in the connective tissue of the fish 102 days post-exposure. The morphology of both actinosporean and myxosporean stages was described by light microscopy and a 1417-bp fragment of the 18S rDNA gene was sequenced. Sequence analysis confirmed the absolute congruence of the two developmental stages and assisted in determining species identity. Host range, tissue specificity and myxospore measurements provided sufficiently distinctive features to confirm species validity and were thus crucial for identification. The triactinomyxon spores had 16 secondary germ cells, unique dimensions, a very opaque sporoplasm matrix and three conspicuously protruding, pyriform polar capsules. This is the first record of a Henneguya sp. life cycle with a triactinomyxon-type actinospore, which suggests a close relationship with the Myxobolus group and a polyphyletic origin of the genus Henneguya.     

Seasonal intestinal coccidiosis in wild bluegill Lepomis macrochirus is associated with a spring bacterial epizootic

Wild bluegill, Lepomis macrochirus Rafinesque, succumb to seasonal mortality in the early spring during cool water temperatures, shown previously to be related to bacteraemia caused by a psychrotrophic bacterium, Pseudomonas mandelii. In the study herein, intestinal coccidiosis in wild bluegill had seasonal prevalence causing heavy intestinal infections and sloughing of intestinal epithelium occurring in late winter/early spring. Infections were predominantly related to two different species, Goussia washuti n. sp., an epicellular coccidium, and a coccidium closely resembling Goussia desseri Molnár 1996, previously only described in percid fish in Europe. In 2019, co‐infections of bacteraemia and intestinal coccidiosis occurred in bluegills. Evaluating coccidium infection intensity by fresh parasite examination and histology, an association was observed in which fish with moderate‐to‐heavy intestinal coccidiosis were 8–12 times more likely to have bacteraemia compared to fish with no or light coccidiosis. The association of these co‐infections suggests that intestinal coccidiosis could contribute to seasonal bacterial epizootics of wild bluegill.     

Myxosporean and microsporidian infections in cultured Pacific bluefin tuna <Emphasis Type="Italic">Thunnus orientalis</Emphasis> in Japan

During the parasitological survey of cultured juvenile Pacific bluefin tuna (PBT) Thunnus orientalis in 2007 and 2008, two myxosporeans and one microsporidian were found. Morphological and molecular analysis showed that the heart-infecting and brain-infecting myxosporeans are identified as Kudoa shiomitsui and K. yasunagai, respectively. This is a new host record for both species. High prevalence of infection (77–100%) with K. shiomitsui was observed in October to December (1–2 months post-transfer to sea cages), whereas only a few fish were infected with K. yasunagai. A microsporidian observed as white “cysts” in the trunk muscle of PBT had a resemblance to Microsporidium seriolae, the causative parasite of beko disease in yellowtail. Phylogenetic analysis showed that the microsporidian from PBT is closely related to but distinct from several other muscle-infecting species such as M. seriolae, Microsporidium sp. RSB, and Microsporidium sp. SH. Additionally, the spore dimension (2.7 × 1.5 μm on average) was remarkably smaller than the others. These results suggest that the present microsporidian is an undescribed species and designated Microsporidium sp. PBT. Prevalence and intensity of infection with Microsporidium sp. PBT reached a maximum of 100% and 20 cysts/fish, respectively. Although pathogenic effects of the two Kudoa species on fish health remain unknown, the microsporidian could be of concern to PBT aquaculture due to unsightly cysts in the musculature, reducing the market value of the fish.     

The significance of myxosporean infections in roach, Rutilus rutilus L., in different habitats

Abstract. Two Myxobolus species, M. pseudodispar and M. ellipsoides , and two Myxidium species, M. rhodei and M. pfeifferi , were found in roach, Rutilus rutilus L., from three different locations in northern Greece, northern England and Scotland. Their prevalence, distribution in the host and pathology were studied. In the ease of M. rhodei , the pathological changes were quantitatively evaluated by computer-based image analysis, and the results expressed in terms of area and volume of organs affected. The pathology of M. pfeifferi was associated with trophozoites in the bile duets and the infection ranged from mild to severe. In the severe eases, degeneration of duetal mucosa sometimes progressed to focal hepatitis. Myxidium rhodei was found in the kidneys as large cysts containing mature and immature spores (Type A cysts), and less often, in the form of small concentric cysts (Type B) which contained no obvious spores but which were characterized by a marked host response giving the appearance of focal granulomas. Type A cysts were also found in liver and spleen, and Type B cysts in the heart. Trophozoites of M. rhodei were observed in only a few eases and occurred in enlarged renal corpuscles in which the capillary tuft was atrophied and compressed. The pathology of M. rhodei was significant due to the enlargement of glomeruli from four to seven times their normal size and with an estimated increase in volume of 54 to 78 times. In addition to the functional damage to the glomeruli, there was also damage of the surrounding interstitial tissue and tubules as a result of the pressure from these enlarged glomeruli. The two myxobolid species were considered to be mainly specific to the kidney with no serious pathology in this organ, but caused significant pathology in the muscles ( M. pseudodispar ) and gills ( M. ellipsoides ).     

Prevalence and development of intraleucocytic haemogregarines from Northwest and Northeast Atlantic mackerel, Scomber scombrus L.

Abstract. Scomber scombrus on both sides of the North Atlantic were infected with similar intraleucocytic haemogregarines. Detection of parasites in blood smears alone was found to be an unreliable indicator of prevalence. In the Northwest Atlantic, prevalence of blood infections varied annually and seasonally, with an average of 18.4%, whereas tissue imprints showed up to 98.3% prevalence. Northeast Atlantic fish had a 4.0% prevalence in blood smears and 100% in spleen imprints. Age 1 mackerel were the principal hosts of haemogregarines in the Northwest Atlantic. Scanty infections of single and paired parasites were observed primarily in lymphocytes and neutrophils of peripheral blood and tissue imprints. Also present in the blood and tissues of Northwest Atlantic mackerel were intracellular schizonts with up to 20 merozoites, and fish from the same region showed haemogregarines within histological lesions in kidney and spleen. Ultrastructural studies on Northeast Atlantic mackerel indicated the parasite is apicomplexan and morphologically dissimilar to Haematractidium scombri. Its relationship with Goussia clupearum was not determined.     

A simplified method to estimate Diphyllobothrium spp. infection in salmonids

Some fish parasites constitute severe management problems as they may cause mortality of their fish host or are important zoonoses of humans. Parasite assessments are therefore critical to keep track of infections. If conventional sampling techniques can be simplified, parasite assessments might be easier to obtain, less time‐consuming and more extensive. In this study, we compare the assessed number of Diphyllobothrium spp. cysts (CYST) with the counted number of Diphyllobothrium spp. plerocercoid larvae recovered using a conventional digestive technique (LARV). The aim was to determine the potential of using CYST as a simplified methodology for assessing Diphyllobothrium spp. infection in salmonids. In total, 365 brown trout and 424 Arctic charr were sampled from nine lakes in subarctic Norway. Strong correlation, significant linear relationship and large amount of explained variation were found between log₁₀CYST and log₁₀LARV in both fish species. The method had a slight, but not significant tendency to work better in charr compared to trout. In addition, absolute difference between CYST and LARV increased at parasite intensities >100 indicating that the method has reduced functionality when estimating parasite intensity in heavily infected salmonid populations. However, overall, using this simplified and less time‐consuming methodology, a good indication of Diphyllobothrium spp. intensity, abundance and prevalence was obtained. We suggest that this method provides a sound proxy of the Diphyllobothrium spp. burden and have the potential to be used in parasite assessment during fish monitoring and fisheries management surveys, particularly if the time and resources for detailed parasite studies are not available.     

Effects of Enteromyxum spp. (Myxozoa) infection in the regulation of intestinal E-cadherin: Turbot against gilthead sea bream

Enteromyxoses are relevant diseases for turbot and gilthead sea bream aquaculture. The myxozoan parasites invade the intestinal mucosa, causing a cachectic syndrome associated with intestinal barrier alteration; nonetheless, their pathological impact is different. Turbot infected by Enteromyxum scophthalmi develop more severe intestinal lesions, reaching mortality rates of 100%, whereas in E. leei-infected gilthead sea bream, the disease progresses slowly, and mortality rates are lower. The mechanisms underlying the different pathogenesis are still unclear. We studied the distribution and expression changes of E-cadherin, a highly conserved protein of the adherens junctions, in the intestine of both species by immunohistochemistry and quantitative PCR, using the same immunohistochemical protocol and common primers. The regular immunostaining pattern observed in control fish turned into markedly irregular in parasitized turbot, showing an intense immunoreaction at the host–parasite interface. Nevertheless, E-cadherin gene expression was not significantly modulated in this species. On the contrary, no evident changes in the protein distribution were noticed in gilthead sea bream, whereas a significant gene downregulation occurred in advanced infection. The results contribute to the understanding of the different host–parasite interactions in enteromyxoses. Host and parasite cells appear to establish diverse relationships in these species, which could underlie the different pathological picture.     

Outbreak of mass mortality of yearling groupers of Epinephelus (Perciformes,Serranidae) associated with the infection of a suspected new enteric Sphaerospora (Myxozoa: Myxosporea) species in South China Sea

A suspected new enteric Sphaerospora species was believed to be directly associated with the mass mortality of yearling groupers of Epinephelus spp. in South China. The epizootic generally emerged from late September to late April of the following year. The infection prevalence and mortality rate were significantly negatively correlated with fish size. Clinical signs included anorexia, cachexia and extrusion of white pulp‐like substance from anus after gentle pressure on the abdomen. Upon necropsy, severe intestinal oedema, thin and transparent intestinal wall, swollen spleen, kidney and gall bladder could be observed. Wet preparation of the infected samples showed large amount of typical disporous plasmodia of the genus Sphaerospora, but no mature spores were observed. Epidemiological investigation showed that this parasite exclusively infected Epinephelus groupers. Histopathologically, this species mainly infected the epithelium of intestine and kidney tubules and caused severe epithelia sloughing and the collapse of intestinal villus. Interestingly, this enteric myxosporidiosis did not cause severe emaciation of infected fish for mass mortality usually emerged within 2–3 days after appearance of clinical signs. The species was most genetically related to Sphaerospora fugu (89% sequence identity) and phylogenetically positioned within marine Sphaerospora lineage. This is the first report of enteric sphaerosporosis of groupers.     

Host susceptibility to Lernaea cyprinacea L. and its treatment in a large aquarium system

Abstract. Host susceptibility to Lernaea cyprinacea was studied during an outbreak of the infection in an aquarium containing 58 species or stocks of fish belonging to 20 families and eight orders. L. cyprinacea was accidentally introduced on two occasions and spread through the recycling of the aquarium exposing all fish to infection. During the first outbreak only 39.7% of the fish species became infected. Approximately 17% carried a mean of less than 10 parasites and 22% carried a mean of more than 10 parasites. During the second outbreak, 6 months after the first, there was a decrease in both the prevalence and intensity of infection; only five species were infected and mean levels of infection were less than 10 per fish except for newly introduced fish. This suggests the possible development of immunity in the previously infected hosts. On both occasions the infection was successfully eradicated by using Unden (2-isopropoxy-phenyl-N-methylcarbamate) at 0.16 ppm, weekly for 4 weeks and Dipterex (0,0-dimethyl, 2,2,2-trichloro-l-hydroxyethylphosphate) at 0.16 ppm for the fifth dose, when the larval stages of the parasite revealed resistance to Unden.